5,243 research outputs found
The NWRA Classification Infrastructure: Description and Extension to the Discriminant Analysis Flare Forecasting System (DAFFS)
A classification infrastructure built upon Discriminant Analysis has been
developed at NorthWest Research Associates for examining the statistical
differences between samples of two known populations. Originating to examine
the physical differences between flare-quiet and flare-imminent solar active
regions, we describe herein some details of the infrastructure including:
parametrization of large datasets, schemes for handling "null" and "bad" data
in multi-parameter analysis, application of non-parametric multi-dimensional
Discriminant Analysis, an extension through Bayes' theorem to probabilistic
classification, and methods invoked for evaluating classifier success. The
classifier infrastructure is applicable to a wide range of scientific questions
in solar physics. We demonstrate its application to the question of
distinguishing flare-imminent from flare-quiet solar active regions, updating
results from the original publications that were based on different data and
much smaller sample sizes. Finally, as a demonstration of "Research to
Operations" efforts in the space-weather forecasting context, we present the
Discriminant Analysis Flare Forecasting System (DAFFS), a near-real-time
operationally-running solar flare forecasting tool that was developed from the
research-directed infrastructure.Comment: J. Space Weather Space Climate: Accepted / in press; access
supplementary materials through journal; some figures are less than full
resolution for arXi
Rapid learning of pursuit target motion trajectories revealed by responses to randomized transient sinusoids
When humans pursue sinusoidal target motion they rapidly learn to track with minimal phase error despite inherent visuo-motor processing delays; prior evidence suggests that prediction might even occur within the first cycle. Here, this has been examined by evoking reactive responses to single cycle stimuli having randomised periodicity and peak velocity. Periodicity was varied within three specific ranges with differing average periodicity. Initial responses in the first half-cycle were remarkably similar within periodicity ranges, irrespective of target velocity or frequency, but differed between ranges. In contrast, in the second half-cycle eye velocity closely matched the target in velocity and timing, irrespective of differences in eye velocity in the first half. Abrupt transitions occurred between first and second half-cycles, consistent with the hypothesis that target motion information is sampled and stored within the first half-cycle, irrespective of actual eye velocity evoked, and then released as a predictive estimate in the second half
Achieving Consistent Doppler Measurements from SDO/HMI Vector Field Inversions
NASA's Solar Dynamics Observatory is delivering vector field observations of
the full solar disk with unprecedented temporal and spatial resolution;
however, the satellite is in a highly inclined geostationary orbit. The
relative spacecraft-Sun velocity varies by ~km/s over a day which
introduces major orbital artifacts in the Helioseismic Magnetic Imager data. We
demonstrate that the orbital artifacts contaminate all spatial and temporal
scales in the data. We describe a newly-developed three stage procedure for
mitigating these artifacts in the Doppler data derived from the Milne-Eddington
inversions in the HMI Pipeline. This procedure was applied to full disk images
of AR11084 to produce consistent Dopplergrams. The data adjustments reduce the
power in the orbital artifacts by 31dB. Furthermore, we analyze in detail the
corrected images and show that our procedure greatly improve the temporal and
spectral properties of the data without adding any new artifacts. We conclude
that this new and easily implemented procedure makes a dramatic improvement in
the consistency of the HMI data and in its usefulness for precision scientific
studies.Comment: 58 pages, 19 figures, submitted to Ap
The role of productive replication in the pathogenesis of murine gammaherpesvirus-68
Murine gamaherpesvirus-68 (MHV-68) is natural pathogen of small free living
rodents. Like Epstein-Barr virus, MHV-68 is B-cell tropic with respect to latency
and sensitive to the anti-viral acyclovir (ACV). The aim of this project was to
evaluate the potency of a new anti-viral called 2'-deoxy-5-ethyl-ß-4'-thiouridine (4'-
s-EtdU) as an inhibitor of MHV-68 replication both in vitro and in vivo. Finally to
utilise the anti-viral activity of 4'-s-EtdU, to be able to study disease associated with
gammaherpesvirus latency in immunocompromised mice, without the complications
associated with lytic virus replication. The potency of 4'-s-EtdU as an inhibitor of
the lytic replication was determined to be 15 times greater than ACV by ECâ‚…â‚€ assay,
giving a value of 0.13μM (35ng/ml). Treatment of infected cell lines lead to the
elimination of detectable productive viral replication. However, virus genomic
DNA, which remained capable of reactivation after treatment withdrawal, was not
eliminated. Not only was this true for cell lines which MHV-68 is known to
establish latency, but also cell lines previously known only to support lytic
replication. The nature of the viral persistence appeared different for the different
cell lines both with respect to virus reactivation after withdrawal of treatment and to
the spontaneous generation of 4'-s-EtdU resistant viral variants. The data leads to
the possibility of MHV-68 being capable of episomal maintenance whilst in a
perpetual state of attempted productive replication. Spontaneously arising 4'-s-EtdU
resistant virus variants were cloned and isolated and found to remained sensitive to
the anti-viral effects of ACV. However, further characterisation of these viral
variants was not undertaken. Treatment of mice with 4'-s-EtdU (0.3mg/ml in
drinking water) from 3 days post infection (in), rapidly eliminated productive virus
replication in the lung tissue, but failed to prevent the establishment and long-term
maintenance of viral latency in the lymphoid compartments. Treatment also failed to
prevent the post acute splenomegaly commonly observed in MHV-68 infected mice.
However, prophylactic treatment of mice prior to infection (in), did prevent virus
dissemination to the spleen as well as preventing splenomegaly. Viral DNA
remained absent from the spleen for as long as treatment was maintained, up to 54 days post infection, as determined by both co-cultivation assay and nested PCR.
However, virus DNA was detected in the lung tissue of the same mice.
Dissemination of virus to the spleen, on withdrawal of treatment correlated with the
production of MHV-68 specific antibodies, as determined by whole virus ELISA.
The experiments provided evidence for both chronic and latent infections of the lung
tissue of the mice infected via the intra-nasal route. The evidence demonstrated the
importance of productive virus replication in the establishment of viral latency in
circulating B-cells and hence development of IM like syndromes even when MHV68 was administered via the intra-peritoneal route. Although 4'-s-EtdU treatment
protected SCID mice from an otherwise lethal MHV-68 infection, it was not possible
to determine the role of productive virus replication in oncogenesis since lymphomas
failed to develop in both long-term infected transiently immunosuppressed, C57BL/6
mice and in SCID mice recipients of syngeneic splenocytes. The study failed to
reproduce the earlier studies (Sunil-Chandra et al, 1993). Surprisingly, viral latency
appeared to be maintained in normal healthy BALB/c mice more efficiently than in
SCID mice transiently repopulated with BALB/c splenocytes. Hence it was not
possible to investigate either the therapeutic benefit or establish the role of
productive virus replication in the development of MHV-68 associated tumour
Interactive Visualization of the Largest Radioastronomy Cubes
3D visualization is an important data analysis and knowledge discovery tool,
however, interactive visualization of large 3D astronomical datasets poses a
challenge for many existing data visualization packages. We present a solution
to interactively visualize larger-than-memory 3D astronomical data cubes by
utilizing a heterogeneous cluster of CPUs and GPUs. The system partitions the
data volume into smaller sub-volumes that are distributed over the rendering
workstations. A GPU-based ray casting volume rendering is performed to generate
images for each sub-volume, which are composited to generate the whole volume
output, and returned to the user. Datasets including the HI Parkes All Sky
Survey (HIPASS - 12 GB) southern sky and the Galactic All Sky Survey (GASS - 26
GB) data cubes were used to demonstrate our framework's performance. The
framework can render the GASS data cube with a maximum render time < 0.3 second
with 1024 x 1024 pixels output resolution using 3 rendering workstations and 8
GPUs. Our framework will scale to visualize larger datasets, even of Terabyte
order, if proper hardware infrastructure is available.Comment: 15 pages, 12 figures, Accepted New Astronomy July 201
- …